Abstract: A capillary zone electrophoresis system with analyte velocity modulation is described. Velocity modulation of the analyte is provided through applying an AC component to the DC driving potential applied to the separation capillary. Typically modulation on the order of 20 to 30% is applied by a separate AC power supply or an integral DC/AC source. Numerous types of detector systems can be employed including refractive index detectors, conductance, fluorescence, etc. The output of the detector is demodulated using a synchronous demodulation. The velocity modulation generates a signal which is a derivative of the conventional concentration/time signal. The system vastly improves detector sensitivity in situations where limitations are imposed by the large and variable background signals which arise from the aqueous buffer itself. Numerous embodiments of means for applying the modulated driving potential are described along with several detectors which can be implemented in systems according to this invention.